Fair Value Measurements - Fair Value Hierarchy for Financial Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2013	Jan. 31, 2013
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total	$ 239,104	$ 21,913
Money market funds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Cash equivalents	222,862	7,637
Commercial paper [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments		2,097
Corporate notes and bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments	15,542	11,479
Certificate of deposits [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments	700	700
Level 1 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total	222,862	7,637
Level 1 [Member] | Money market funds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Cash equivalents	222,862	7,637
Level 1 [Member] | Commercial paper [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments
Level 1 [Member] | Corporate notes and bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments
Level 1 [Member] | Certificate of deposits [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments
Level 2 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total	16,242	14,276
Level 2 [Member] | Money market funds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Cash equivalents
Level 2 [Member] | Commercial paper [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments		2,097
Level 2 [Member] | Corporate notes and bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments	15,542	11,479
Level 2 [Member] | Certificate of deposits [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments	700	700
Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total
Level 3 [Member] | Money market funds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Cash equivalents
Level 3 [Member] | Commercial paper [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments
Level 3 [Member] | Corporate notes and bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments
Level 3 [Member] | Certificate of deposits [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Short-term investments